1. Field of the Invention
The invention relates to a method of allocating communication resources in an MF-TDMA telecommunication system, in particular, although not exclusively, a system using a transparent geosynchronous satellite.
2. Description of the Prior Art
It is known in the art that diverse types of communication resources, in particular frequencies, time slots and codes, can be used to transmit a multiplicity of digital calls simultaneously.
Multiple frequency time division multiple access (MF-TDMA) transmission, which uses a multiplicity of frequencies and time slots simultaneously, provides a high data bit rate. This is why it is used in the DVB-RCS standard, currently in preparation, which concerns the transmission via satellite of digital data (audio, video, Internet, etc.).
In the above type of telecommunication system, each carrier, which has a particular frequency, offers a given number of time slots per frame, the number of time slots per frame being equal to 1 or to a power of 2, for example (4, 8, 16, 32, 64, 128 time slots per frame).
Messages are transmitted in superframes containing a particular number of frames. A frame, which comprises a particular number of carriers and time slots, is transmitted during a particular time and a superframe extends over a number N of frame durations and includes a number N1 of carriers.
During a frame, the same message may be transmitted on several different types of carrier, that is to say with time slots of different duration.
As a general rule, MF-TDMA calls can be “star” calls, i.e. calls made through the intermediary of a base station. In other words, a terminal communicates with another terminal via the base station. It is also possible to effect calls directly between terminals, without passing through the base station, and this type of call is called a “meshed” call. It is also possible to combine star calls and meshed calls.
It has been found that, for real-time data, star or meshed MF-TDMA transmission can cause errors. In the case of video signals the errors can be visible and in the case of audio signals the errors can be audible. It has been found that these errors are the result of temporal instability (jitter), leading to inaccuracy in the times separating the various packets of the same call.